The approach to improve confidence in Services Implementation presented in this paper is based on the addition of a Service Modeler and Verifier Function (SMV) in the environment where the service take place. The SMV, combined with a test scenario, is able to detect on-the-fly implementations errors. The SMV keeps an abstract model of the service and the environment in which the service is executed and verifies at each model change properties derived from the requirements. In order to update its model the SMV spies all messages between the different entities of the network. The properties are expresses in linear time temporal logic. This paper presents the concept of the SMV and its realization for the CS-1 Intelligent Network.